From one of our veggie gardening experts:

Leave them be. Heads should develop although varieties vary in their heat tolerance.

Cauliflower is a "heavy feeder." Consider fertilizing plants lightly with a complete, balanced fertilizer (has roughly equal percentages of nitrogen, phosphorous, and potassium).

Also, when the heads start to form they can use rubberbands to hold the leaves together to protect the heads from intense sunlight. This is mainly an issue for varieties with floppy leaves. Many newer varieties have tight wrapper leaves that help cover and protect the heads.

Also see:
Growing Cauliflower in a Home Garden | University of Maryland Extension (umd.edu)

This is a link to a site which has not been vetted by the UnMD but you may find it useful: 

11 Reasons for Cauliflower Not Forming Heads | Gardener’s Path (gardenerspath.com)

Good luck
Len